DOT1L induces RNAPII accumulation independent of its catalytic activity in pluripotent stem cells

Pluripotent stem cells can be propagated in vitro from embryos in specific culture conditions that capture subtle developmental transitions. Naive pluripotent mouse embryonic stem cells (ESCs) can exist in two distinct epigenetic states--the metastable state in serum/LIF conditions and the ground state with pharmacological inhibition of differentiation-inducing pathways in the 2i/LIF conditions, which better resembles the in vivo blastocyst. Here, we acutely induced one feature of 2i/LIF ESCs, an increase in the H3K79 methyltransferase, DOT1L, in serum/LIF ESCs to determine its effects on metastable pluripotency. We find that DOT1L induction causes an increase in RNA Polymerase II (RNAPII) accumulation at the transcription start site, irrespective of catalytic activity, mimicking 2i/LIF RNAPII pattern. However, the pulse of DOT1L and consequent RNAPII accumulation is insufficient to induce immediate changes in steady-state or nascent RNA expression. Genes with higher transcription and elongation rates exhibit moderate changes in RNAPII accumulation, while lowly transcribed genes separate into two distinct groups, with one group showing the strongest RNAPII accumulation in response to DOT1L induction and the other showing the weakest. This differential accumulation is reduced at H3K27me3-enriched and bivalent genes. We also find that cells that sustain DOT1L expression have a homogenous NANOG protein profile without affecting Nanog transcription. Taken together, we find that a pulse of DOT1L in serum/LIF ESCs is sufficient to partially recapitulate certain features of ground state pluripotency, reinforcing its importance in this state of the pluripotency continuum.